Plant oils are used in a variety of applications. Novel vegetable oil compositions and improved means to obtain oil compositions, from biosynthetic or natural plant sources, are needed. Depending upon the intended oil use, various different fatty acid compositions are desired.
Higher plants appear to synthesize fatty acids via a common metabolic pathway—the fatty acid synthetase (FAS) pathway. In developing seeds, where fatty acids are attached to glycerol backbones, forming triacylglycerides, for storage as a source of energy for further germination, the FAS pathway is located in the plastids. The first committed step is the formation of acetyl-ACP (acyl carrier protein) from acetyl-CoA and ACP catalyzed by the enzyme, acetyl-CoA:ACP transacylase (ATA). Elongation of acetyl-ACP to 16- and 18-carbon fatty acids involves the cyclical action of the following sequence of reactions: condensation with a two-carbon unit from malonyl-ACP to form a β-ketoacyl-ACP (β-ketoacyl-ACP synthase), reduction of the keto-function to an alcohol (β-ketoacyl-ACP reductase), dehydration to form an enoyl-ACP (β-ketoacyl-ACP dehydratase), and finally reduction of the enoyl-ACP to form the elongated saturated acyl-ACP (enoyl-ACP reductase). β-ketoacyl-ACP synthase I catalyzes elongation from C4:0 up to palmitoyl-ACP (C16:0), whereas β-ketoacyl-ACP synthase II catalyzes the final elongation to stearoyl-ACP (C18:0). Common plant unsaturated fatty acids, such as oleic, linoleic and linolenic acids found in storage triacylglycerides, originate from the desaturation of stearoyl-ACP to form oleoyl-ACP (C18:1) in a reaction catalyzed by a soluble plastid Δ-9 desaturase (also often referred to as “stearoyl-ACP desaturase”). Molecular oxygen is required for desaturation in which reduced ferredoxin serves as an electron co-donor. Additional desaturation is effected sequentially by the actions of membrane bound Δ-12 desaturase and Δ-15 desaturase. These “desaturases” thus create polyunsaturated fatty acids.
Obtaining nucleic acid sequences capable of producing a phenotypic result in FAS, desaturation and/or incorporation of fatty acids into a glycerol backbone to produce an oil is subject to various obstacles including but not limited to the identification of metabolic factors of interest, choice and characterization of an enzyme source with useful kinetic properties, purification of the protein of interest to a level which will allow for its amino acid sequencing, utilizing amino acid sequence data to obtain a nucleic acid sequence capable to use as a probe to retrieve the desired DNA sequence, and the preparation of constructs, transformation and analysis of the resulting plants.
Thus, additional nucleic acid targets and methods for modifying fatty acid compositions are needed. In particular, constructs and methods to produce a range of different fatty acid compositions are needed.